Aurora police spokeswoman Cassidee Carlson says officers searching the grounds of the Promenade at Towne Center Apartments on Friday night found the boy under water and immediately performed CPR.
The boy, whose name has not been released, was taken to a hospital and was pronounced dead a few hours later.
The Denver Post reports investigators are trying to determine who was caring for the child when he went missing.
(Copyright 2012 by The Associated Press. All Rights Reserved.)